michael.c

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/*
 * Michael MIC implementation - optimized for TKIP MIC operations
 * Copyright 2002-2003, Instant802 Networks, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/types.h>
#include <linux/bitops.h>
#include <linux/ieee80211.h>
#include <asm/unaligned.h>

#include "michael.h"

static void michael_block(struct michael_mic_ctx *mctx, u32 val)
{
    mctx->l ^= val;
    mctx->r ^= rol32(mctx->l, 17);
    mctx->l += mctx->r;
    mctx->r ^= ((mctx->l & 0xff00ff00) >> 8) |
           ((mctx->l & 0x00ff00ff) << 8);
    mctx->l += mctx->r;
    mctx->r ^= rol32(mctx->l, 3);
    mctx->l += mctx->r;
    mctx->r ^= ror32(mctx->l, 2);
    mctx->l += mctx->r;
}

static void michael_mic_hdr(struct michael_mic_ctx *mctx, const u8 *key,
                struct ieee80211_hdr *hdr)
{
    u8 *da, *sa, tid;

    da = ieee80211_get_DA(hdr);
    sa = ieee80211_get_SA(hdr);
    if (ieee80211_is_data_qos(hdr->frame_control))
        tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
    else
        tid = 0;

    mctx->l = get_unaligned_le32(key);
    mctx->r = get_unaligned_le32(key + 4);

    /*
     * A pseudo header (DA, SA, Priority, 0, 0, 0) is used in Michael MIC
     * calculation, but it is _not_ transmitted
     */
    michael_block(mctx, get_unaligned_le32(da));
    michael_block(mctx, get_unaligned_le16(&da[4]) |
                (get_unaligned_le16(sa) << 16));
    michael_block(mctx, get_unaligned_le32(&sa[2]));
    michael_block(mctx, tid);
}

void michael_mic(const u8 *key, struct ieee80211_hdr *hdr,
         const u8 *data, size_t data_len, u8 *mic)
{
    u32 val;
    size_t block, blocks, left;
    struct michael_mic_ctx mctx;

    michael_mic_hdr(&mctx, key, hdr);

    /* Real data */
    blocks = data_len / 4;
    left = data_len % 4;

    for (block = 0; block < blocks; block++)
        michael_block(&mctx, get_unaligned_le32(&data[block * 4]));

    /* Partial block of 0..3 bytes and padding: 0x5a + 4..7 zeros to make
     * total length a multiple of 4. */
    val = 0x5a;
    while (left > 0) {
        val <<= 8;
        left--;
        val |= data[blocks * 4 + left];
    }

    michael_block(&mctx, val);
    michael_block(&mctx, 0);

    put_unaligned_le32(mctx.l, mic);
    put_unaligned_le32(mctx.r, mic + 4);
}